Torque limiting device



Dec. 12, 1950 w. C. STARKEY 2,533,973

TORQUE LIMITING DEVICE Original Filed Nov. 1, 1943 2 Sheets-Sheet l 1 15. l w 2 I H3 H5 INVENTOR.

' Mum/1 meuro/vJrflz/mr Dec'. 12, 1950 w. c. STARKEY 2,533,973

TORQUE LIMITING DEVICE Original Filed NOV. 1, 1945 v 2 Sheets-Sheet 2 22.1 Zn '0 "1 15.5 ""FIEi. "Pl

PI 11 22 i Zz INVENTOR.

Patented Dec. 12, 1950 2,533,973 'EGBQUE LIMITING DEVICE William Carleton Starkey, Indianapolis, lnd., as-

signor to Fletcher Trust Company, trustee, Indianapolis, Ind, a corporation Original application November 1, 1943, Serial No. v

598,651, new Patent No. 2, i59,9fl2;, dated Ila-nuary 25, 1949. Divided and this application July 12,1947, Serial No. 769,669

(oi. e -st) 19 Claims.

This invention relates to a torque limiting spring clutch device, this being a division of my application for Letters Patent Serial No. 508,601, filed November 1, 1943, entitled Torque Limiting Device, now Patent No. 2,459,972, dated January 25, 1949.

The invention is particularly useful and applicable in maintaining a non-slipping friction driving connection between driving and driven members up to a predetermined driving torque while enabling slippage upon imposition of overload, torque.

For. example, the invention may be, applied to stud, nut and screw drivers, bottle cap applicators, tapping devices and like tools, wherein it is desired that the stud, nut, screw, cap or the like, is to be applied under a predetermined torque for proper setting. The invention may similarly be applicable to power devices, such as are einployed in engine starters, road working machinery, stokers and the like to protect the operating parts against damage due to excessive overload.

The three illustrated embodiments of subject invention are of the internal drum type in which at least one of the two (driving and driven) members served by the clutch spring has an internal clutching surface against which the clutching coil portions of the spring are normally expanded or seated by inherent spring force so that the spring will be self-energized, and the spring has enough coils to enable transmission of toruue far above the desired limit. As explained in my aforesaid patent, overload rejection is accomplished by enabling a predetermined amount of angular relative movement of said members which, in turn, causes sufiicient contraction of: the seated spring to enable continued slippage between it and the drum surface or surfaces involved during continuance of the overload. Non-slipping is resumed automatically as soon as the imposed torque falls below the overload value.

The said angular relative movement in the instant invention is permitted by conjoint action of a minor clutching coil portion of the spring designed to initially slip on its coacting drum surface as the overload point is reached and a special flexible hence torque sensitive coil portion which operates to enable the major clutching coil portion to remain in full clutching engagement up to the instant slippage of the minor portion occurs.

The special flexible coil portion is normally substantially bypassed by the torque forces imposed on the clutch, which is to say it is protected from. subjection thereby to substantial flexing. strain until overload and said initial slippage of the minor portion occurs. The yielclable; load sensitive element (indicating an important object), has to carry only a minor fraction oi the load desired to be transmitted, wherefore said element can, for example, be a peripherallyrelieved and thus reduced section portion of a suitable simple helical clutch spring wound from uniform section stock.

Another feature of the invention resides in so arranging a torque limiting spring clutch that limited torque may be transmitted in either direction through a single clutch spring.

Still further feature of the invention residesin adjusting the angular relation of the riving and driven members such as to vary the extent of the angular displacement therebetween required to unload the load transmitting coils of. the spring. By means thereof the maximum driving torque permitted by the device may be varied.

The full nature of the invention will be understood from the accompanying drawings and the, following description and claims:

Fig. l is a longitudinal sectional view throu h the device with parts thereof shown in elevation.

Fig. 2 is a section taken on the line 2-2 of Fig. 1

Fig. 3 is a section taken on the line 3-3 of Fig. 1.

Fig. 4 is the same as Fig. 1, showing a modified form of the invention.

Fig. 5 is the same as Fig. 1, showing a fur: ther modified form of the invention.

Fig. 6 is a side elevation of one of the driving elements of Fig. 5.

Fig. 7 is an end elevation of the driving elementof Fig. 6.

Fig. 3 is an end view of the clutch spring of Fig. 5.

Fig. 9 is a side elevation of the clutch spring. shown in Figs. 5 and 8.

Fig. 10 is a section taken on the line Ill -l0 of Fig. 5.

Fig. 11 is a plan view of the adjusting key of Fig. 5.

In Figs. 1 to inclusive, there is shown one modification of torque limiting device wherein there is provided a driving member comprising a shaft it, and a driven member comprising a shaft ll provided with a driven pocket. Ha. having a cylindrical internal clutch surface l2. The driving member It may be driven from any suit- .I able source of power or by hand, and through the torque limiting device drives the driven member or pocket I la on the driven shaft ll up to a preof by a retaining ring it, whereby the driving shaft has its bearing within said sleeve at one end of the pocket. Adjacent the other end thereof, the end of the driving shaft is provided with a reducedspindle i rotatable in a bearin sleeve Eta mounted within a reduced bore of the pocket.

The clutch spring l6 surrounds the driving shaft it and is embraced within the pocket Ha for self-energizing clutching engagement with the internal clutch surface thereof under its inherent spring force. One end of the clutch spring it is secured to a helical torque transmitting collar il having a shoulder against which the load carrying end is of the spring abuts, bein re movably secured thereto by a locking member #9. Said collar H is mounted for free rotation within the pocket Ila and is keyed to the driving shaft It to bear against a thrust shoulder of the pocket I la.

Said spring 56, being normally in clutching engagement with the clutch surface I2, upon a driving torque being applied to the shaft It) in the direction of the arrow, said spring will be rotated by the collar H in the clutching direction or to maintain its expanded clutching engagement within the pocket to normally provide a positive driving connection between the driving and driven members. Upon the torque being applied in the other or declutchin direction, the clutch will freely overrun.

At the opposite unloadin end of the spring it, as shown in Fig. 3, there is provided an undercut recess having a shoulder 2i. Extending into said recess for movement into abuttin en- 7 gagement with said shoulder there is a deenergizing or unloading element in the form of a pin 22.

Said pin is normally out of engagement with said shoulder during normal driving action.

The load sensitive flexible element of said device is in the form of a reduced coil or relieved portion of the clutch spring, as indicated at 23. It carriesonly a fraction of the total load. To permit its load limiting action, its clearance relative'to the pocket must be such that the coil never expands into complete engagement therewith at the maximum load to be transmitted, This load sensitive element is of such physical characteristics that in association with the load carrying coil indicated at a, they will Withstand normally applied torque load, but upon overload sufficient to slip the load carrying coil and flex the coil 23 outwardly, the driving and driven members will be angularly displaced relative to each other. Such angular displacement causes the unloading element in-the form of the pin 22 to engage the unloading end of the clutch spring in the form of the shoulder 2!, and as the relative movement between the unloading element and spring is in the direction of the arrow of Fig. 3, said element tends to unload the spring in a wrap down direction sufiiciently to permit such slippage as to prevent the excess load from being transmitted there through.

As a result of this actionythe non-slipping driving connection between the driving and driven members is released as to any torque being transmitted therebetween above the predetermined load, controlled by the load sensitive element or relieved coil'of the spring. However, upon the overload being removed or relieved, the inherent stresses in the clutch spring, and particularly the relieved load sensitive portion thereof, will return it to normal non-slipping clutching engagement with the clutch surface to transmit the driving torque up to its normal predetermined maximum.

From the above, it will be observed that the clutch spring embodies a load carrying coil at its load carrying end, as indicated at a. Therelieved coil 23 permits the coil a to slip independently of the other clutching coils and slippage of the coil a permits the. coil 23 to flex as the overload is approached. Upon full overload such slippage and flexing results in sufficient angular displacement to unload the remaining coils of the spring between the load sensitive coil and the unloading end of the spring at 28. These coils act in the nature of load transmitting coils which assist the load carrying coil in transmit tin the torque up to the overload. Said load transmitting coils each carry less and less of the load transmitted as they approach the unloading end 2i. displacement will increase and the clutching action of the load transmitting coils will be progressively reduced from the unloading end to the load sensitive coil. In this manner the clutch sprin acts to transmit torque within the maximum permitted, but not beyond. The predetermined maximum torque at which the device will drive, is, therefore, governed by the clutching power of the load carrying coil a in conjunction with the flexibility of the load sensitive coil 23 and the degree of angular displacement between the pin 22 and shoulder 2! required to unload the load transmitting coils. 7

One advantage of this action resides in the load sensitive element, or coil 23 being by-passed by the torque transmitting character of the load transmitting coils and the load carrying coil a Thus, only a fraction of the torque load is carried by the coil 23.

In the modification of the torque limiting device shown in Fig. 4, a driving member in the form of the shaft HE! rotating in the direction of the arrow is adapted to drive the driven member ill. The member HI is provided with a driven pocket having an internal cylindrical clutch surface H2.

ternal cylindrical clutch surface 1M adapted to abut and mate with the surface H2, The clutch spring i i6 is mounted within the abuttin pockets and is normally expanded into clutching engagement with their respective clutch surfaces. This arrangement is referred to as a split or double pocket type of torque limiting device, the split being indicated at l 55. Thus, at the split N5 the clutch pockets may rotate relative to each other. However, the clutch spring, being in normal clutching engagement with both pockets, posi tively transmits the driving torque from one to the other through the load carrying coil which spans the split I I 5.

At the anchored end of the spring Hi5 it is provided with a toe iii extending laterally into a recess iii; formed in the pocket M3 to lock therewith. At the other or unloading end of said spr'ng, the shaft He carries an' unloading or deenergizing element in the form of a pin I22 A As the overload increases, the angular The driving member has keyed thereto a driving pocket i I3 having an in- 5 freely movable within a recess formed in the underside of the spring adjacent its unload ng end and which .is movable into engagement ,with

theshoulder l2i formed thereby, in the manner illustrated in-Fig. 3. The load sensitiveelement, as abovedeseribed in connection with Figs. 1, 2, and 3,. comprises the reduced coil or relievedportion.=fathe spring, as indicated at ['23. .Said relieved portion. .23 ispreferably located at approximately one. coil removed from the .load carrying co'il which spans the splitii'lfiybetween the pockets, and is spaced inwardly ifrom the driven pocket. Thus, vivi'th the springin normal clutching ,eng'agement relative tosaid pockets, the full load carryingcoil spans the split .l i .and the additional .load transmitting coils in clutching engiagement with the clutch suriiace ofth'e driven poeketare separated therefrom lay the (relieved coil I423; said loadtransnritting coils each carryii'ig'less and lessof thelc-ad transmitted asthey approach the unloading. end! 2 i.

The operation of this split pocket form of torque -limitingdevioe is similar in all respects to, thatabove described, in that the driven pocket is positively connected to the :driving pocket through the action of all theclutching coils of the spring for transmitting normal driving torque. Upon the torqueloadbecomingzexcessive 611169110 overload the spannin .loadxcarrying. coil willhe caused to slipwandperrnitithe loadsensitive coil toafleXh ther-eoy permitting :angular "displacement between the driving and -.driven. members. This permits the-lpin -i.22-to.engage the shoulder 121 to more theluhloadingwendrof the springinia direction tendingtowrap down the load transittingkooils to permit, s usage thereof relative tetheblutch suri aceii and therebycrelease the drive-njmember fromthe driving member to the extent of. the overload.

Inthe lllOdlfifiCl,fOIIIlHIOfslFhS invention illustrated, inciliigs. L5 to, 11, inclusive, the torque limiting device; is ai angedtoi provide a dual, action v-herein the overloadwelease may become :effective when driven .in either direction. ,RVhen driven in the direction, of the arrow, the driving membeigcomprises the-shaft Eli), and the driven member comprises the shaft 2 i i withiits :pocket to providetheclutch so aceillli. Klheshaftfilfi is supported byi the bearing sleeves ,2 It, and 21 '4 carried in the pocketof the shaft 2H. Torque is .t ansj te et e n a t e. rivi and driven Inc bersby the-clutch s pring 2 ?l5 normallyuin ing ,-.engageinent with ,the clutch surface ad-s flaft iiltihaskeyed theretoythe oppos dispose h l torq :tra smittinecolm 2-16 nd zlfl, each being provided with a laterally ofi f set shoulder 2-18 against which the respective ends gorthe clutch sprin -2 l5. abut. llachlof said c lars-is provided with a lreyway 2 58 whereby, it is heyedto the shait ziiiandeach is provided W e 1 2 3 fo f iv w fitt ne de mre o load n W 1 i x e di g out r ly Hemlin p e S rin jace t eaeir of th opposed ends thereof. Said pins-22 i are of. lesser diameter; than their-respective receiving holes, 229 so that they have "free play-therein.

The load sensitive, flexible element, as in i the preceding modifications comprises one or the other of apairioi reduced. orrelievedportions or coils of the spr ing, as indicated at ZZZ and 223, th re bei 91 6 51 .9 i p liQ i a h of -the, coils next adjacent' the end coils of the rin -j "ea den w l i met nt ha eabl is el e sar rinsto en the u oadin endin e hsema eQtdr va By means of this arrangement, upon thedriv ing shaft Zlilbeing rotatedinthe direction of the arrow, the torque transmitting collar 21-6 abutting the end of. thespringatllfi, willtransmit the full torque tothat-endof thespring, tending to expandthe spring into tighter clutchingengagement .With the pocket of thethendriven member ZI I. or ue f th shaf 1 H! d e t vto said member 21 l. However, upon an overload bein applied, theload carrying coil will slip and th'e load sensitive element inv the form or the relieved coil 22: of, thespring adjacent the collar .2; I 5, which always carries only adractionof ,the total load, Will be caused to hex outward-1y toward the .pocketand thereby permit of the angular displacementrbetween; theshaftfi; ill and; the unloadin end of the clutch spring which abuts the collar 231. Such displacement. will causethe collar,2 H, which then becomes the deenergizing" or unloading element, tomove relativato the end of the spring abutting therea ainsuuuntilthe free plavbetween itspin 2;2i the ho1e 22il in saidwllar is taken up. Thereupon. further displacement causes said end of thespringtobepulled ing a direction, tending to wrap it downirorn; its normal clutching engagement :with the clutch gsurf ace of theepocketfof the shaftdl-Land thereby permit, slippage as long as the overload is applied.

,On the other' hand, wherein the .shait-2 ifi .-is driven in the opposite direction .to that shown in the arrow. the reverse actiontakes place. ll-hue, the collar 2 F? Will act totransmittorque through abutting engagement. withthe spring at 21 8, and upon overload the load sensitive element 223 adjacent the collar-2H will be -flexed to permitthe angular displacement above referred to. The play between the pin and hole in the collar 2-11 willbe taken :up and said collar will pull the unloading end of the .spi'ing suiliciently to wrap it down out of its normal clutching engagement. Thus, in. this form of the invention the overload becomes effective irrespective of the directionof drive of the driving member.

As shown in Figs. '5 and 11, the shaft Kilt provided with a keyway 225:1"01' receiving an adjusting key 25. Said key is slidalole longttudinally of the shaft through a corresponding heywaviin the bearing sleeve 2E3 and the collar M5. Thebase of the key isstraight, as shown in Fig. 11. However, the upper portion of the key which slides in the collar HE is angled, as indicated at 22?, so that as the key is causedto slide upon the shaft, its angularengagement with thecollar issuch as to shift the collar peripherally relativeto the shaft. This adjustment is such as to caueea slight angular displacement between the collar 215, on the one hand, and all of the otherelements, including the shaft 2M and collar-.211. -Sueh displacement varies the relation of the unloading pinizl relative to the collar 25'! so that it has a greater or lesser movementbeiore the unloading action beeornes effective. The result of such'displacement is that a greater or lesser torque load will required to flex the load sensitive element in order to unload or wrap the spring down to permit slippage.

From the foregoing, it will be observed that in respect to the various .modificaticns there is involved in each of them a clutch spring having; one or more coils -.or portions thereof relieved or. reduced in diameter for acting as the load sensitiveselementin associationwith a loadcarrying coil orcoils. -,Whereas, the load sensitive ele nentis herein shown as so. relieved portiomoi Said spring thereby transmits the driving,

the spring, it may comprise a portion of such diameter as to permit free play relative to the clutch surface and of such character or formation as to flex for permitting slippage of its associated load carrying coil resulting in angular displacement between the ends of the spring or members upon an overload. Such angular displacement acts to bring into play a deenergizing or unloading element, herein shown in the form of a collar or fpin connected with the driving member, which tends to unload or deenergize that end of the :spring associated therewith to permit slippage of the entire spring relative to the clutch surface sufficient to disconnect the positive driving connection between the driving and driven memlbers.

Whereas, the several modifications of the invention are shown herein for purpose of illustration as embodying a spring having an external clutching surface, the invention is equally applicable to modifications wherein the clutch spring is of a character having an internal clutching surface. Furthermore, it is unimportant as to whether or not the load carrying end of the spring or its unloading end is connected with the driving member or the driven member, the same principle of operation as above described being equally effective, wherein the clutch spring has a portion thereof adapted to slip and flex upon overload to permit of angular displacement between its load carrying and unloading ends.

The invention claimed is:

1. A torque limiting device including a driving member, a driven member, one of said members being provided with a clutch surface, a clutch spring having expansible and 'contractible coils normally in friction clutching engagement with said clutch surface including an unloading end and a load carrying coil spaced therefrom and connected with the other of said members through Which a driving torque will be transmitted, a non-clutching coil of the spring adjacent the load carrying coil normally locked thereby against flexing but rendered free to flex upon slippage of the load carrying coil to permit angular displacement of said members, and a deenergizing element on the said other said member operable by said angular displacement to move into deenergizing engagement With the unloading end of said spring tending to progressively unload the coils thereof to the extent that said non-clutching coil is flexed, and thereby limit the clutching capacity of said spring to a predetermined maximum torque load.

2. A torque limiting device including a driving member, a driven member, one of said members being provided with a clutch surface, a clutch spring having expansible and contractible coils normally in friction clutching engagement with said clutch surface, said spring having a load carrying portion operably connected with the other of said members through which a driving torque will be transmitted, a load sensitive portion embodied in said spring between the ends thereof adapted to limit the load carrying capacity of said load carrying portion and flex upon slippage thereof. under an overload torque to permit angular displacement of said members, and a deenergizing element on the member to which said spring is operabl connected movable upon angular displacement of said members to deenergizing engagement with the other end of said spring tending to progressively unload the coils thereof to the extent that said load sensitive portion isflexed, thereby limiting the clutching members, a load sensitive free floating coil embodied in said spring adjacent the load carrying portion thereof adapted to flex upon slippage of said portion under an overload torque, to permit angular displacement of said members, and a deenergizing projection on said rotatably mounted member movable upon said angular displacement for deenergizing engagement with said spring tending to progressively unload the clutching coils thereof to the extent that said load sensitive portion is flexed, and thereby limit the clutching capacity of said spring to a predetermined maximum torque load.

4. A torque limiting device including a driving member, a driven member, one of said members being provided with a clutch pocket in which the other member is rotatably mounted, said pocket having an internal clutch surface, a clutch spring having a series of expansible and contractible coils normally in clutching engagement with said clutch surface under inherent spring tension, said spring having a load carrying coil engaging the said pocket adapted to slip upon overload and a load sensitive coil spaced from said pocket to permit flexing and slippage of the load carrying coil, the latter coil being operably connected with the other said member, to permit angular displacement of said members upon an overload torque, and a deenergizing element on said rotatably mounted member movable upon said angular displacement for deenergizing engagement with said spring tending to progressively unload the clutching coils thereof to the extent that said load sensitive portion is flexed, and thereby limit the clutching capacity of said spring to a predetermined maximum torque load.

5. A torque limiting device including a driving member, a driven member, said members being provided with coaxial aligned and adjacent cylindrical clutch surfaces, a clutch spring having expansible and contractible' coils normally in positive clutching engagement with said clutch surfaces including a load carrying portion spanning said adjacent surfaces for transmitting driving torque therebetween, one end of said spring being operably connected with one of said members and the other end of said spring being free floating to provide an unloading end, a load sensitive portion embodied in said spring adjacent said load carrying portion and spaced from one' of the clutch suriaces adapted to flex under an overload torque to permit angular displacement of said members upon slippage of said load carrying portion, and a deenergizing element operable by said angular displacement to engage the floating unloading end of said spring tending to pro- 7 gressively unload the coils thereof to the extent that'said load sensitive portion is flexed, and

thereby limit the clutching capacity of said spring to a predetermined maximum torque load.

6. A. torque limiting device including a driving member, a driven'member, said" members bein provided With-opposed cylindrical poc zets having aligned clutch: surfaces, a clutch spring having expansible andcont-ractible coils normally in friction clutching engagement with saidclutch surfaces including a loadoarrying portion spanning the'adjacent ends of said pockets for transmit" ting driving torque therebet'ween, one end of said spring being operably connected with the pocket of one of said members andthe other end'of said springbeingifree floating to provide anunloading end within the other of said pockets, a load sensi tive portion embodied in said spring adjacent said load carrying'portion and spaced from one of the clutch surfaces adapted to flex under an overload torque to permit angular displacement of said pockets upon slippage of said load carrying portion, and a deenergiaing element operableby said angular displacement to engage the unloading end of said spring tending to progressively unload the coils thereof to the extent that said load sensitive portion is flexed; and thereby limit the clutching capacity of said spring to a pre demrmined maximum torque load.

'7. A torque limiting device including a driving member, a driven member, one of said members being provided with a clutch surface, a clutch spring having expansible and contractible coils normally in friction clutching engagement with said clutch surface, torque transmitting elements on the other of said members in operative driving engagement with opposite ends of said spring respectively, a free play connection between the ends of said spring and their respective torque transmitting elements, and a load sensitive portion embodied insaid spring adapted to flex under an overload torque to permit angular displacement of said members, one of sa d elements acting to transmit torque when the driving memher is rotated in one direction and the opposed element acting to transmit torque when said member is rotated in the opposite direction, said free play connection of the non-torque transmit.- ting element acting to unload said spring upon said load sensitive portion being flexed.

8. A torque limiting device including a driving member, a driven member, one of said members being provided with a clutch surface, a clutch spring having expansible and contractible coils normally in friction clutching engagement with said clutch surface, torque transmitting elements on the other of said members inoperative driving engagement with opposite ends of said spring respectively, a free play connection between the ends of said spring and their respective elements, a load carrying coil adjacent each end of said spring, and a re ieved load sensitive coil adjacent each ioad carrying coil adapted to iiex under an overload torque to permit angular displacement of said members, one of said elements acting to transmit torque when the driving member is rotated in one direction and the opposed element acting to transmit torque when said member is rotated in the opposite direction, the non-toroue transmitting element acting to unload said spring through its free play connection therewith through said axial displacement upon the load sensitive coil adjacent the lead carrying coil being flexed.

9. A torque limiting device including a driving member, a driven member, one of said members being with a clutch surface, clutch spring having ex ansibe and contractible coils normally in fric n clutching engagement with said clutch surface, torque transmitting means onthe other of said members in driving engagement with opposite ends of said spring, respectively, a free play connection between the ends of said spring and their respective torque transmitting means, a load carrying coil" adjacent each end of said spring, a relieved load sensitive coil adjacent each load carrying coil adapted to flex under anovei'loacl torque to permit angular displacement of said members, one of said torque transmitting means acting to transmit: torque when the driving member is rotated in one direction and the opposed said means acting to transmit torque when said member is rotated in the opposite direction, the non-torque transmitting means acting to unload said spring through its free play connection therewith upon said angul r displacement of said members and to the exent that the load sensitive coil adjacent the load carrying coil is flexed, aligned keyways in one of members and its torque transmitting means, and an angularly formed key adjustable in said keyways to effect angular adjustment therebetiveen to vary the extent of angular displacement required for unloading said spring to correspondingly vary the maximum torque load transmitted therethrough.

10. A torque limiting device including a driving member, driven member, one of said members I? provided with a clutch surface, a clutch mg having expansible and contractiole coils normally in friction clutching engagement with said ciutch surface, a torque transmitting elet on the other of said members in driving engagement with the load carrying end of said spring, a free play connection between said lastentioned her and the unloading end of said mg, a load sensitive portion embodied in said spring adjacent the load carrying end thereof adapted to flex upon slippage of said load carrying end. under an overload torque to permit anguiar displacement of said members, said free play connection acting to unload said spring to the extent that said load sensitive portion is flexed, a igned keyways in said element and last-mentioned member, and an angularly formed driving hey adjustable in said keyways to effect axial ad'- justment therebetween and thereby vary the exent or". angular displacement required for unoading said spring to correspondingly vary the maximum torque load transmitted therethrough. ii. A torquelimiting device including a driving member, a driven member, one of said members being provided with a clutch engaging surface, a clutch spring normally in cutching engagement with said surface, a load sensitive element intermediate the other of said members and a portion of clutch spring through which driving torque is transmitted, unloading means carried by said last mentioned member movable to unload said spring to permit slippage relative to clutch surface upon said lead sensitive ele ment yie ding under an overload to permit axial displacement between said members, and an adtable connection between said last mentioned member and spring for varying the angular relation of said members and the extent oi angular displacement required to cause said unloading cut to be effective. 1 A torque limiting device including a driving inei her, a driven member, one of said members provided with a clutch engaging surface, a clutch spring having a series of expansible and contractible coi's normally in clutching enga ment with said surface, one end of said spring being operably connected with the other said member, a load sensitive element effective under an overload torque to permit angular displacement between said members, an unloading el ment carried by said last mentioned member engagable with the other end of said spring upon said angular displacement tending to unload said spring and permit slippage relative to said clutch surface, and means for adjusting the connection between said last mentioned member and spring for varying the extent of angular displacement between said members required to unload said spring.

13. A torque limiting device including a driving member, a driven member having a clutch engaging surface, a clutch spring having a series of expansible and contractible coils normally in clutching engagement with said clutch surface and having an unloading end, a load sensitive element adjacent the other end of said spring operably connected with said driving member for permitting axial displacement between said members upon an overload torque being applied thereto, an unloading element carried by said driving n iember movable into operative engagement with the unloading end of said spring in a direction to unload said spring and cause it to slip rela tive to said clutch surface, and a driving connection between said driving member and the driven end of said spring adjustable to vary the angular relation of said members to correspondingly vary the efiective overload torque.

14. A torque limiting device including a driv ing member, a driven member, one of said memhere being provided with a clutch surface, a clutch spring having expansible and oontractible coils normally in friction clutching engagement with said clutch surface and including an unloading end, a load carrying coil operably connected with the other of said members through which driving torque is transmitted in the clutching direction, a flexible load sensitive element between said first mentioned coils and said load carrying coil adapted to cooperate with said load carrying coil to flex and permit slippage thereof upon an overload torque to effect angular displacement or said members, and a deenergizing element on said other said member operable by said angular displacement to move into operative engagement with the unloading end of said spring and cause it to slip relative to said clutch surface.

15. A torque limiting device including a driving member, a driven member, one of said members being provided with a clutch surface, a clutch spring having expansible and contractible coils normally in friction clutching engagement with said clutch surface and including an unloading end, a load carrying coil operably connected with the other of said members through which driving'torque is transmitted, a freely flexible load sensitive element between said first mentioned coils and said load carrying coil adapted to cooperate with said load carrying coil to hex and permit slippage thereof upon an overload torque to effect angular displacement of said members, a deenergizing element operable by said angular displacement movable into operative engagement with the unloading end of said spring and cause it to slip relative to said clutch surface, and

driving connection between said driving member and clutch spring adjustable to vary the angular relation thereof to correspondingly vary the effective overload torque.

'16. A torque limiting clutch adapted to couple a driving member to a driven member, and Whele* in a peripheral clutching surface is co-rotative with one of the members and a helical clutch spring having major and minor clutching portions is co-rotative with the other member in a clutching direction for gripping engagement with the clutching surface, said minor portion having a limited torque transmitting engagement therewith, characterized by a yielding torque sensitive element between said clutching portions, said torque sensitiv element and minor portion operating conjointly to enable relative angular movement of said members during imposition thereon of overload torque, and means on said other member movable with said relative angular movement into deenergizing engagement with said major portion to eifect torque limiting deenergization of the clutch.

17. A torque limiting clutch adapted to couple a driving member to a driven member, and wherein a peripheral clutching surface is co-rotative with one of the members and a helical clutch spring having a plurality of load carrying coils forming the major portion of said spring and a lesser number of load carrying coils comprising the minor portion of said spring, said spring being co-rotative with the other member in a clutching direction for gripping engagement with the clutching surface through said major portion, and through said minor portion within the limits of a predetermined overload torque, said spring being characterized by a yielding torque sensitive coil intermediate said major and minor portions yieldable upon slippage of said minor portion to permit conjointly therewith relative angular movement of said members during imposition thereon of overload torque, and means on said other member movable with said relative angular movement into deenergizing engagement with the end coil of said major portion to effect torque limiting deenergization of the clutch.

18. In a torque limiting clutch adapted to couple a driving member to a driven member, and wherein a peripheral clutching surface is co-rotative with one of the members, and a helical clutch spring having major and minor clutching portions co-rotative with the other member in the clutching direction for gripping engagement with the clutching surface, the combination of a torque sensitive connection between said major and minor portions operative to enable relative angular movement of said members upon imposition of overload torque in the clutching direction, a clutch spring deenergizing device on the'said other member rendered operative by such relative angular movement to move into declutching engagement with said major portion, said device being partially controlled by slippage of said minor portion, and said minor portion providing a driving connection between said major portion and one of said members in parallel or torque by-passing relation to the torque sensitive connection whereby to transmitpart of the torque that would otherwise be transmittedby the latter connection alone.

19. A torque limiting spring clutch, comprising a rotary clutch drum, a coaxial rotary member, a helical clutch spring one end of which is operatively connected to said rotary member in a manner to cause the spring to turn always with the rotary member in one direction, the spring having a series of coils at the opposite end in frictional clutching normal-torque-transmitting engagement with the drum, the terminal coil at that end of the spring being free and having a deenergizing shoulder whereby the coils of said series may be progressively withdrawn from 13 clutching engagement with th drum to enable the clutch to reject an overload, the spring having a maximum-load-carrying clutching coil por tion and a non-clutching torque sensitive coil portion both located between said series of coils and the connected first mentioned end of the spring, said two coil portions being operative conjointly, one by slippage on the drum and one by resistance to deflection under torque to enable relative angular movement between the rotary member and the drum while engaged with said series of coils, and abutment means connected with said rotary member and engageable with said deenergizing shoulder in a manner to cause said progressive withdrawal of coils of said series out of clutching engagement with the drum.

WILLIAM CARLETON STARKEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 10 Number Name Date 1,126,780 Jones Feb. 2, 1915 1,561,537 Hayes Nov. 17, 1925 2,360,187 Almen Oct. 10, 1944 

